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Last modified: 21 December 2023


Introduction to CIAO Tools and Applications

New to X-ray Astronomy?

For those new to X-ray astronomy and data analysis, please see our "An X-ray Data Primer: What I Wish I Knew when Starting X-Ray Astronomy"

CIAO is a data analysis system written for the needs of users of the Chandra X-ray Observatory. Because Chandra data is 4-dimensional (2 spatial, time, energy) and each dimension has many independent elements, CIAO was built to handle N-dimensional data without concern about which particular axes were being analyzed. Also, apart from a few Chandra instrument tools, CIAO is mission independent.

CIAO also needed to be able to filter and project the 4-D Chandra event data to managable sizes and convenient arrays. This has to be done flexibly, so we have built all CIAO tools to take a filtering and binning specification on the command line, making use of a general-purpose regions syntax.

Since Chandra data can be sliced and diced in so many ways, and because the Chandra calibration is spatially and energy dependent, we needed to keep track of just how the data had been filtered and binned, which we do in a "data subspace". The tools keep track of this subspace automatically and allow users to review previous data processing.

The CIAO design allows close interconnection of tools. For example, the output of any of the source DETECT programs can be fed into dmextract to create a summed spectrum which can then be fit in Sherpa.

The modeling and fitting tool Sherpa is central to the CIAO system. Sherpa performs forward fitting of models to data in N dimensions. The Sherpa website has information on how to use this application.

Data visualization is provided by the DS9 application for viewing images, interacting with Astronomy databases (including using SAMP to send and receive tables and images between applications and web pages), and displaying tables, and the matplotlib plotting package for display in Sherpa and python analysis sessions.

In order to allow users of Chandra data to use pre-existing tools, all CIAO tools read and write several formats, including FITS images and tables (which includes event files) and several types of ASCII files (e.g. space, comma, or tab-separated columns).

Altogether CIAO is a powerful system for the analysis of many types of data.

Further Information